What Is a Lie Detector?

Polygraph Tests Measure Changes in The Body Under Questioning

A lie detector, or polygraph instrument, is a combination of medical devices used to track physiological changes that occur in the body as an individual is being questioned on a particular issue. During the questioning session, the examiner watches how the person’s heart rate, blood pressure respiratory and electro-dermal activity behave, with reference to baseline levels. Fluctuations can uncover that the person is being deceptive. The results of the exam are subject to interpretation, which is why it is crucial that the operator is experienced.

Lie detectors are designed to identify significant involuntary responses that may be going on in the body of an individual when he or she is subjected to stress; such as the stress that comes with deception. The tests do not specifically point out that an individual is lying, but rather that the physiological responses of the body are signalling a stress reaction. Deception may relate to something unrelated to the question being asked. The polygraph examiner has to ask further questions to decide if any stress or deceptive behaviour being exhibited is conclusively related to the question being asked.

The importance of qualified examiners in the lie detection process cannot be overemphasised. This is why over the counter lie detectors in the hands of untrained individuals can end up doing more harm than good.

Polygraph Lie Detection

Polygraph exams are often associated with criminal investigations. However, there are other scenarios where they come into their own. For example, people can be subjected to a polygraph exam before they are hired for a sensitive job role, such as a security job in government. Some private-sector employers also request that potential employees undergo a polygraph exam.